1. Field of the Invention
The present invention relates to an alignment layer of liquid crystal display device, and more particularly, to an apparatus for forming an alignment layer of liquid crystal display device.
2. Description of the Related Art
Because of the recent developments in various portable electronic devices, such as mobile phones, PDAs and notebook computers, the demand for a light, thin, small flat panel display device is increasing. Research is actively ongoing on several types of flat panel display devices including LCD (Liquid Crystal Display), PDP (Plasma Display Panel), FED (Field Emission Display), VFD (Vacuum Fluorescent Display) and other technologies. Of the aforementioned flat panel display devices, the LCD has received much attention because it is simple to mass produce and can be easily used with a driving system that implements a high quality picture.
FIG. 1 is a cross-sectional view of a related art liquid crystal display device. As shown in FIG. 1, a liquid crystal display device 1 includes a lower substrate 5, an upper substrate 3 and a liquid crystal layer 7 formed between the lower substrate 5 and the upper substrate 3. The lower substrate 5 is a driving unit array substrate that includes a plurality of pixels (not shown). Each of the pixels includes a driving unit, such as a thin film transistor. The upper substrate 3 is a color filter substrate that includes a color filter layer for implementing color in the liquid crystal display.
Pixel electrodes 9 are formed on the lower substrate 5 in FIG. 1. A common electrode 11 is formed on the upper substrate 3. Alignment layers 13 and 15 for aligning liquid crystal molecules in the liquid crystal layer 7 are respectively disposed on the pixel electrodes 9 and on the common electrode 11.
The lower substrate 5 and the upper substrate 3 are attached by a sealing material 17. Further, the sealing material 17 maintains and the liquid crystal layer 7 between the lower substrate 5 and the upper substrate 3. The liquid crystal molecules of the liquid crystal layer 7 are driven by driving units (not shown) formed on the lower substrate 5. The pixel electrodes 9 are connected to driving units (not shown). The quantity of light transmitted through the liquid crystal layer 7 is controlled by voltages supplied by the driving units (not shown) and applied across the liquid crystal layer 7 using the pixel electrodes 9 to display information visually.
FIG. 2 is a flow chart of a method for fabricating a liquid crystal display, device according to the related art. The fabrication process of the liquid crystal display device is roughly divided into a driving unit array substrate fabrication process for forming a driving unit on the lower substrate 5, a color filter substrate fabrication process for forming the color filter on the upper substrate 3, and a panel fabrication process. The panel fabrication process occurs after the color substrate fabrication process and the driving unit array substrate fabrication process.
As shown in FIG. 2, step S101 of the driving device array fabrication process includes forming a plurality of gate lines and a plurality of data lines on the lower substrate 5 to define a plurality of pixel areas, forming of thin film transistors in the driving areas, and forming driving devices that are connected to the gate lines and the data lines. In addition, the pixel electrodes 9, which are connected to the thin film transistors, are formed for driving a liquid crystal layer in response to a signal transmitted through the thin film transistor.
Step S104 of the color filter substrate fabrication process includes forming a color filter layer on the upper substrate. The color filter layer has R, G and B colors. A common electrode is then subsequently formed on the upper substrate.
Steps S102 and S105 of both the driving unit array substrate fabrication process and the color filter substrate fabrication process include formation of alignment layers on the upper and lower substrates. The alignment layers are rubbed in a specific direction. The alignment layers provide an initial alignment and surface fixing force (i.e., pre-tilt angle and orientation direction) to the liquid crystal molecules of the liquid crystal layer formed between the upper and lower substrates.
Step S103 includes scattering a plurality of spacers onto the lower substrate for maintaining a uniform cell gap between the upper and lower substrates. Step S106 includes formation of a sealing material along an outer portion of the upper substrate. Thus, as described above, steps S101 to S106 depict the color substrate fabrication process and the driving unit array substrate fabrication process.
As shown in FIG. 2, step S107 of the panel fabrication process includes attaching the upper and lower substrates by compressing the upper and lower substrates together. Step S108 of the panel fabrication process includes dividing the attached upper and lower substrates into a plurality of individual liquid crystal panels. Step S109 of the panel fabrication process includes injecting the liquid crystal material into the liquid crystal panels through a liquid crystal injection hole, and then the liquid crystal injection hole is sealed to form the liquid crystal layer. Step S110 of the panel fabrication process includes testing the injected liquid crystal panel.
Operation of the LCD device makes use of an electro-optical effect of the liquid crystal material, wherein anisotropy of the liquid crystal material aligns liquid crystal molecules along a specific direction. Accordingly, control of the liquid crystal molecules significantly affects image stabilization of the LCD device. Thus, formation of the alignment layer is critical for fabricating an LCD device that produces quality images.
FIG. 3 is a schematic view of a method for forming an alignment layer using a roller coating method according to the related art. In FIG. 3, an alignment material 21 is uniformly supplied between an anylox roll 22 and a doctor roll 23 as the anylox roll 22 and the doctor roll 23 rotate. The alignment material 21 is provided using a dispenser 20 having an injector shape. Then, the alignment material 21 formed on a surface of the anylox roll 22 transfers onto a rubber plate 25 when the anylox roll 22 rotates while contacting a printing roll 24 upon which the rubber plate 25 is attached. A mask pattern is formed on the rubber plate 25 to selectively print the alignment layer on the substrate 26. The mask pattern of the rubber plate 25 is aligned with a substrate 26 upon which the alignment material 21 will be applied.
As a printing table 27, upon which the substrate 26 is loaded, is moved to contact the printing roll 24, the alignment material 21 is transferred onto the rubber plate 25 and is then subsequently transferred onto the substrate 26 to form an alignment layer. The thickness of the alignment layer is about 500 Å (angstroms) to 1000 Å (angstroms). However, a thickness variation of 100 Å (angstroms) in the alignment layer may generate a blot on the screen of the LCD device. Accordingly, an alignment layer having a uniform thickness is critical to display quality images on the screen of the LCD device.
The dispenser 20 supplies the alignment material 21 between an anylox roll 22 and a doctor roll 23 using a sweeping left-to-right motion along at an upper part of the anylox roll 22. As a result, the dispensing in a sweeping left-to-right motion, the thickness of the resulting alignment layer may not be consistent. As a size of the substrate 26 increases, it becomes increasingly more difficult to form the alignment layer having a uniform thickness. For example, the thickness at the side edges of the alignment layer corresponding to the ends of the sweeping left-to-right motion is different than the middle of the alignment layer.
Since all of the alignment material 21 transferred on the rubber plate 25 is not necessarily transferred onto the substrate 26, a significant amount of the alignment material 21 is wasted as compared to the amount of alignment material 21 that was transferred onto the substrate 26. Accordingly, the amount of wasted alignment material 21 unnecessarily increases production costs. Further, a cleaning process must be periodically performed that complicates processing and degrades productivity. In addition, when the size of the substrate changes because of the need to produce another model, the roll (doctor roll, anylox roll, printing roll) must be replaced. Furthermore, as the substrate is enlarged in size, the size of the roll printing device (i.e., the anylox roll and the printing roll) is increased. That is, the large substrate needs the corresponding large equipment, and in this case, it is difficult to maintain a uniform thickness of the alignment layer.